chenistry

Monday, June 6, 2011

-organic compounds that are comprised elements other than carbon or hydrogen (ex. nitrogen & oxygen)

-tend to be the most reactive part of the molecule

types of functional groups: alcohols, halides, aldehydes, ketones

Halides & Nitro Compounds

-naming: close to that of simple hydrocarbons - can be fixed to alkanes, alkenes, & alkynes (end w/-ANE)

-if there is more than 1 of the SAME halogen/molecule attached to 1 molecule, add the prefix di, tri, tetra, penta, etc. before the halogen/molecule prefix

-if there are DIFFERENT halogens/molecules attached to 1 molecule, list the positions in alphabetical order

(ex. 2,4,4-tribromo-5-chlorononane)

-the main chain name obtains one of these prefixes that are fixed to it

Halogens

Molecules

F

Fluoro

NO2

Nitro

Cl

Chloro

Br

Bromo

I

Iodo

Ex. 1 (top left):

# of carbon atoms: 1 à methane

# of halogens: 3 Cl in the first carbon position à tricloro

Ex. 2 (top right):

# of carbon atoms: 1 à methane

# of halogens: 4 Cl in the first carbon position à tetrachloro

Ex. 3 (below):

***Note: each empty corner represents ONE carbon atom, thus there are 2 carbons in this molecule! :D

2 carbons = ethane

1 Cl attached in the first carbon position (recall: there isn’t a set direction in which to count the position that the carbon is in; count from the whichever way creates a smaller #, in this case, from left to right)

This compound is called 1-chloroethane or simply chloroethane.

Properties of Halides

-tend to be insoluble in H2O

-compounds combined with fluorine are non-reactive (inert)

Ex. Teflon, which makes up the thin non-stick surface on frying pans

-compounds containing chlorine or bromine are more reactive under extreme conditions

-compounds that have iodine are quite reactive; they can be easily substituted with other functional groups

Properties of Nitro Compounds

-often insoluble in H2O

-inert to chemical attack unless under extreme conditions

-generally explosive

Ex. TNT (trinitrotoluene & nitroglycerine)

-most smell pleasantly fruity

Alcohols

-have an –OH (hydroxyl) functional group

-naming: use the longest carbon chain containing the OH group & replace the ‘e’ ending in the parent hydrocarbon with ‘ol’

-remember: always use the smallest # possible for the OH group even if the branched parts will get a higher # (ex. 4-methyl-2-pentanol rather than 2-methyl-4-pentanol)

Tuesday, May 31, 2011

Even though they both form bonds that contain fewer Hydrogen atoms attached to Carbon atoms, THEY ARE VERY DIFFERENT!
Naming these compounds are relatively easy, as they follow the same rules as naming Alkanes. Just remember to change the ENDING to the appropriate one!

Let's start with Alkenes.

Alkenes-->contain one or more double bonds
-->classified as unsaturated hydrocarbons
-->CHANGE ENDING TO "-ENE"

eg. CH3-CH2-C=CH-CH3
|
CH3-CH3-CH3

2-propyl-2-pentene

*notice how the ending of the parent chain changed

Alkenes have a many possible structures (same), BUT have different geometrical shape
-->this is special to ONLY ALKENES called geometric insomers

scientific study of the structure of carbon-based compounds and hydrocarbon

can vary from small to large

has a specific naming system

different kinds of structures to represent a molecular formula

form chains of carbon atoms

Properties:

A carbon that has 4 bonds

A carbon atom that has 4 hydrogen atoms

A carbon-carbon bond

Branched Chain

Rings

Naming:

There are certain names for each molecular formula!

1 - meth

2 - eth

3 - prop

4 - but

5 - pent

6 - hex

7 - hept

8 - oct

9 - non

10 - dec

You use these prefixes in the beginning and the endings for alkanes is “-ane.”

The formula is CnH2n+2, if you plug in the numbers and it doesn’t work then that means that it is not from the alkane group!

When looking at the structures: Always look at the longest chain and write the molecular formula from there!

For example:

It is called Propane because there are three of the longest chain.

For the Alkayl group, they have a different formula and different naming system:

The ending is “-yl,” so an example would be methyl.

For example:

This structure is called 3-methyl-pentane because the bond is on the third position and it is called methyl because it is from the alkyl group. It is called pentane because the longest chain has 5 of them.

Extra facts: The sum of all valence e- of each atom in the molecular formula must equal the number of electrons in your Lewis Dot Structure.

Except for a few elements, ex. H, most elements want a full valence shell.

Electrostatic Force
Electronegativity: the measure of the ability of an atom to attract electron from other atoms.Metals have LOW electronegativityNon-metals have HIGH electronegativity
*The greater the difference of electronegativity, it is more likely to be Ionic Bond ENeg Diff. = | ENeg1- ENeg2 |

Sunday, May 15, 2011

The Lewis Structure involves using dots. It is very simple and easy to understand!

Here are some examples!

Number of Valence Electrons

1

2

3

4

5

6

7

8

Example

Hydrogen

Group I
(Alkali metals)

Helium

Group II
(alkali earth metals)

Group III

Group IV

Group V

Group VI

Group VII
(Halogens)

Group VIII except Helium
(Noble Gases)

Lewis Structure
(electron dot diagram)

That is what Lewis structures look like and how the dots are formed with the symbol in the middle to identify which element it is. The purpose of the Lewis Structure is that it shows the valence electrons that are distributed in a molecule. Also there is a rule called the octet rule which is saying that most of the atoms want the electrons to form covalent bonds. This rule does not necessarily apply to all of the atoms.

Here is an example of H20!

Here are some practice ones!

H

● ●

NH4 + = H ● N● H

● ●

● ●

H

The first step is to first draw 4 H’s because the element is H4.

Then you write a N in the middle with the surrounding H’s because it is the only element and it only has one.

The third step is to then daw two dots for every H surrounding the N.

You apply the same rules and the same procedure for the other elements.

Thursday, April 21, 2011

The above was definitely NOT proper English.It's actually something called Electronic Configuration.Today, you're going to learn how to write "chemists' gibberish".Looking forward to it?

What is electronic configuration?-description of an atom's orbitals & how many electrons occupy each orbital-helps to group & learn about the elements of the periodic table

recall: Niels Bohr suggested that electrons occur only in particular energy states - when an electron emits/absorbs a particular amount of energy, it will instantly jump to a different orbital

important terms to know:

-energy level: amount of energy that an electron is able to have 'n' is the # of the energy level -for a given value of 'n', different types of orbitals are possible n=1 only s-type is possible n=2 s- & p-types are possible n=3 s-, p-, d-types are possible n=4 s-, p-, d-, f-types are possible

-quantum: the difference of energy of 2 specific energy levels

-ground state: when all the atom's electrons are in the lowest possible state (ie. stable, like a noble gas)

-excited state: when all the atom's electrons are temporarily occupying an energy state greater than its ground state ex. When an electron takes in extra energy, like a photon, or hits a neighbouring particle, it becomes excited.

-orbital: the actual area of space that an electron occupies in a specific energy level -4 types: s, p, d, & f -energy levels are not spaced apart evenly -each orbital is symbolized by a circle

-shell: group of all orbitals with the same n-value ex. 3rd shell: 3s, 3p, 3d orbitals

-sub-shell: group of orbitals with the same type ex. group of 5 3d-orbitals of the 3d shell

Type of subshell

# of orbitals

Max. # of electrons

s-type

1 s-orbital

2

p-type

3 p-orbitals

6

d-type

5 d-orbitals

10

f-type

7 f-orbitals

14

order in which the orbitals are filled:

Writing Electronic Configurations for Atoms

Neutral atoms:-always begin using the LOWEST energy-determine the # of electrons (recall: in a neutral atom, the atomic # is the # of electrons), then start at 1s, continuing to add until there are no more electrons-each electron has an opposite spin classified by up & down arrows

potassium: 19 electrons

***NOTE: FOR EACH ORBITAL, DRAW ALL THE UP ARROWS FIRST FROM LEFT TO RIGHT BEFORE PAIRING THEM WITH THE DOWN ARROWS!!!***

Ions:-negative ions: add electrons (equal to the charge) to the final unfilled subshell, starting from where the neutral atom left off-positive ions: start with the neutral configuration & take away electrons from the OUTERMOST shell first

Exceptions

Why are you so surprised?! There are always exceptions!!

Cr (Chromium gains stability with a HALF-FULL d-subshell)

we would predict: 1s2 2s2 2p6 3s2 3p6 4s2 3d4

but it is actually -->1s2 2s2 2p6 3s2 3p64s13d5

Cu (Copper gains stability with a FULL d-subshell)

we would predict: 1s2 2s2 2p6 3s2 3p6 4s2 3d9

but it is actually -->1s2 2s2 2p6 3s2 3p6 4s1 3d10

Core Notation

-special type of electron configuration: core electrons are replaced by the nearest noble gas -usually take part in chemical reactions-outer electrons: outside of the core electrons (ie. the noble gas)

How to write core notation

1. locate the atom & the nearest noble gas at the end of the period ABOVE the element (it is crucial to use the noble gas in the PREVIOUS row!!!)

2. replace the first part of the electron configuration (core) with the matching noble gas with the noble gas' symbol in square brackets